Non cutting hole-shaping and thread-forming stainless screw and process with impact for driving in the same

ABSTRACT

A hole-shaping and thread-forming screw ( 1 ) has a non-cutting hole-shaping end section ( 2 ) that ends in a point, a haft section ( 4 ) provided with a thread ( 3 ) and an engagement section ( 5 ). The non-cutting hole-shaping end section ( 2 ) tapers towards its end. The whole screw is made of a stainless material, in particular its end section ( 2 ). When the screw ( 1 ) is driven in, a hole is haped without cutting into the workpiece ( 7 ) and is then threaded by the screw ( 1 ) itself.

BACKGROUND OF THE INVENTION

The invention relates to a hole-shaping and thread-forming screw with anon-cutting hole-shaping end section that ends in a point or apoint-like shape, a shaft section provided with a thread, and anengagement section for attaching or inserting a tool, as well as amethod for driving in a hole-shaping and thread-forming screw.

In the case of thread-shaping screws, which drill their own hole orshape it without cutting, it was standard procedure until now tomanufacture the hole-shaping end section of a material that could behardened, in other words carbon steel. In most instances, expensivesolutions were provided, if the head and partial sections of the shafthad to be manufactured from a stainless material. In addition, weldingsolutions were used, where a drill tip of material that could behardened, in other words carbon steel, was welded to the other region ofthe screw.

This not only requires several work steps, it also results inparticularly high manufacturing costs.

The present invention has therefore set itself the task of creating apossibility, for a screw made of stainless steel, of shaping a hole withthis screw, without having to use welding solutions with differentmaterials.

According to the invention, it is proposed that the non-cuttinghole-shaping end section, which narrows at an acute angle towards theend, relative to the screw axis, is formed of a stainless material.

Screws with the embodiment explained initially have become known invarious embodiment variants. For example, in U.S. Pat. No. 2,015,159, afastener is shown and described, which has a nail tip and acorresponding thread on the shaft. By hitting the screw with a hammer,the tip is forced through a thin metal sheet, and subsequently it isdriven in by means of a corresponding rotational movement of thethreaded section. This combination of a nail and a screw was surelymanufactured of a carbon steel at the time of the application, sincethere was probably no idea of stainless attachment elements at thattime. From EP-B1 0 464 071, a hole-shaping and thread-forming screw isknown, which has a hole-shaping part that narrows, where the screw ismade in one piece of annealed steel. By means of rotation of the screw,friction surfaces are formed between the screw and the sheet metal to bepassed through, so that the metal sheet is heated in such a way that thematerial is brought into its plastic range, in that it becomes soresilient in the radial direction that the desired hole expansion withmaterial displacement to form a nozzle occurs. In this embodiment, also,an attempt was made to reach a solution with a carbon steel.

With the present invention, the possibility is created, for the firsttime, of shaping the hole for the thread-cutting screw with acorresponding end section made of a stainless material. Until now, itwas considered impossible, by persons skilled in the art, to shape ahole with a screw made of a stainless material. Rather, it was alwaysassumed that a drilling process or a corresponding high level ofheating, up to the plastic range, was required, in order to be able todrill or simply shape a hole. A person skilled in the art had to assume,until now, that a drilling process with corresponding “cutting edges”made of stainless steel is completely impossible, and that the use ofcarbon steel, in other words annealed steel, is required for shaping ahole without using drill blades.

SUMMARY OF THE INVENTION

The present invention has therefore overcome a prejudice of personsskilled in the art, because it was made possible to shape the hole witha screw made of stainless material, and furthermore also a stainless endsection, to form the thread, and therefore to be able to use a fastenerwhich is entirely formed of stainless material.

Therefore it is also a particular characteristic, according to thepresent invention, that all the sections of the screw are entirely madeof a stainless material.

It is possible that a stainless steel is used as the stainless material,or that light metals or alloys of light metals, i.e. alloys with a majorproportion of light metals, e.g. brass, copper, aluminum, or similarmetals, are used as the stainless material. Depending on the specificpurpose of use, the structure according to the invention results in veryspecific possibilities of use of a screw made of a special material. Forexample, it has now become possible to make the material selection withmutual adaptation of the work piece and the screw, without any specialwelding solutions or the attachment of drill plates of differentmaterials being required.

For the hole-shaping end section, various embodiment variants arepossible, with different design variants resulting as a function of thematerial of the work piece and, of course, as a function of the materialof the screw. For example, it is possible that the non-cuttinghole-shaping end section is formed from two or more partial sectionswith different angles relative to the screw axis. In this connection, itis also possible that the non-cutting hole-shaping end section is madeto be triangular or polyangular, circular, ellipsoid, of a constantdiameter, or similar in cross-section.

It is particularly advantageous if a special method is used to drive thescrew in. According to the invention, it is proposed in this regard thatwhen the screw is driven in to shape the hole in non-cutting manner, anaxial impact effect is exerted on the screw in addition to therotational drive. It has been shown that the additional impact effect isparticularly advantageous, specifically when using screws made ofstainless material, and that it results in rapid penetration of the workpiece without significant heat development.

Furthermore, the additional process step that the impact effect on thescrew acts only during the hole-shaping process and is eliminated duringthe thread-cutting process and while the screw is driven into thethread, is advantageous. In other words, once the hole has been shaped,the impact effect is removed, so that the thread can be formed inoptimum manner. This results in an optimum fit, particularly duringthread forming, and the fact that the hole wall has been partiallyelastically deformed during the preceding hole-shaping process alsocontributes to this fit, so that now this hole wall is more or lessresiliently pressed against the thread.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics according to the invention and specialadvantages will be explained in greater detail in the specificationbelow, on the basis of the drawing. This shows:

FIG. 1 a view of a screw when used to penetrate a work piece;

FIG. 2 a cross-section through the work piece and the screw after thethread has been formed in the previously shaped hole.

FIGS. 3a and 3 b are similar to FIG. 1 and illustrate alternativeembodiments in accordance the invention, having trapezoidally shapedpoints.

DESCRIPTION OF PREFERRED EMBODIMENTS

The screw 1 consists, for one thing, of an end section 2 that ends in apoint or a point-like shape, a shaft section 4 provided with a thread 3,and an engagement section 5 for attaching or inserting a tool. The endsection 2 is provided in order to shape a hole 6 in a work piece 7,without cutting, whereupon the shaft section 4 provided with a thread 3forms the thread in the shaped hole 6, i.e. into the hole delimitationwall 8 which extends downward.

The non-cutting hole-shaping end section 2 is formed to narrow at anacute angle towards the screw axis 9. The essential characteristic ofthe screw 1 is to be seen, however, in the fact that it is made of astainless material. In this connection, this has been taken so far thatall the sections 2, 4, and 5, in other words the entire screw 1, areentirely made of a stainless material.

A version of a stainless steel can be used as the stainless material,or, of course, light metals or alloys of light metals, i.e. alloys witha major proportion of light metals, can be used. For example, it ispossible that such screws 1 according to the invention be made of brass,copper, aluminum, or similar metals. Within the scope of the invention,it is also possible to make such screws of plastic, wherecorrespondingly strong plastics can be used, in order to shape holes andform threads in work pieces made of plastic, for example, or of lightmetal, or in corresponding steel sheets.

The special design structure of the end section 2 is possible in severalvariants. In the embodiment shown, a simple cone tip is provided. It isalso possible, however, to make this non-cutting hole-shaping endsection 2 pyramid-shaped or, for example, in the shape of a truncatedcone or a truncated pyramid. In experiments, it has been shown that itis not absolutely necessary for an extreme point to be formed at the endsection 2, in order to achieve the proper effect of hole shaping.Several cross-section variants are also possible for the non-cuttinghole-shaping end section 2. For example, the cross-section could betriangular or more than triangular, circular, ellipsoid, of a constantdiameter, or a similar shape. It would also be possible that theimmediate “tip” itself could be circular, ellipsoid, of a constantdiameter, or a similar shape when seen in a top view. It is advantageousif such a screw is driven in using a special method. The time for holeshaping is significantly reduced, if an axial impact effect is exertedon the screw when the screw is driven in to shape the hole innon-cutting manner. In other words, by using a corresponding rotationaldrive with an impact effect in the axial direction, shaping of the holecan be brought about much more quickly. In itself, it would be possibleto superimpose an impact that acts in the direction of rotation on therotational drive, but this has no influence on the effectiveness and theperiod of shaping.

It is particularly advantageous if no impact effect is present any moreafter shaping the hole for the subsequent thread-forming process andwhile the screw is driven in, so that only the necessary rotationaldrive is present. This results in a significantly better fit in the workpiece.

The screw shown in FIG. 1 is a relatively short screw with a threadedsection 4 which follows a cylindrical section 10, and a subsequent,thread-free section 11 which reaches to the engagement section 5. Themeasures according to the invention can, of course, be used for screwsof all lengths, and have a positive effect particularly in the case ofvery long screws, since in many instances long screws, specifically, areto be made of stainless material. It is also possible to continue thethreaded section 4 over the entire length of the screw shaft, or toprovide several threaded sections consecutively, with spaces betweenthem, where the threaded sections can also have different diameters.

What is claimed is:
 1. Hole-shaping and thread forming screw forpiercing and fastening material and having a longitudinal axis, a firstend and a second end, comprising: a non-cutting hole-shaping end sectionat said first end having a non-circular cross-section and a taperedsurface for piercing a hole in said material when said screw is driven;a shaft section connected to said first end section and provided with acutting thread for threading said hole by cutting a thread in a sidewall of said hole when said screw is driven; and an engagement sectionat said second end for attaching or inserting a driving tool, the firstend section of the screw narrowing at an acute angle relative to thescrew axis, and said entire screw being of a stainless material. 2.Screw according to claim 1 wherein stainless steel is the stainlessmaterial.
 3. Screw according to claim 1, wherein alloys with a majorproportion of one of brass, copper, and aluminum are the stainlessmaterial.
 4. Screw according to claim 1, wherein the non-cuttinghole-shaping end section has at least two partial sections withdifferent angles relative to the screw axis.
 5. Screw according to claim1, wherein the non-cutting hole-shaping end section is one oftriangular, polyangular, and ellipsoid in cross-section.
 6. A method ofdriving in a hole-shaping and thread forming screw having a longitudinalaxis, a hole-shaping section and a thread forming section, the entirescrew being a non-hardened stainless material, comprising the steps: (a)driving said screw into a material in a direction of said axis to shapea hole with said hole-shaping section in said material in a non-cuttingmanner; (b) rotating said screw about said axis during step (a); (c)impacting said screw in said direction of said axis during step (a); (d)cutting a thread in said shaped hole with said thread forming section tomake a threaded hole; and (e) driving said threaded section into saidthreaded hole.
 7. The method of claim 6 wherein said axial impacting isexerted only during said hole shaping.
 8. A workpiece in combinationwith a hole-shaping and thread forming screw comprising: the screwhaving a longitudinal axis, a first end and a second end, being of anon-hardened stainless material; a non-cutting hole-shaping end sectionat said first end including a tapered surface for piercing a hole in theworkpiece when the screw is driven; a shaft section connected to saidfirst end section and provided with a cutting thread for threading thehole by cutting a thread in a side wall of the hole when the screw isdriven; an engagement section at said second end for attaching orinserting a driving tool, the first end section of the screw narrowingat an acute angle relative to the screw axis; and the screw beingthreadedly engaged with the workpiece in a hole made by said first end.9. The invention according to claim 8 wherein stainless steel is thestainless material.
 10. The invention according to claim 8 whereinalloys with a major portion of one of brass, copper, and aluminum arethe stainless material.
 11. The invention according to claim 8 whereinthe non-cutting hole-shaping end section has at least two partialsections with different angles relative to the screw axis.
 12. Theinvention according to claim 8 wherein the non-cutting hole-shaping endsection is one of triangular, polyangular, circular, and ellipsoid incross-section.